Camshaft adjusters are used in internal combustion engines to vary the timings of the combustion chamber valves in order to be able to vary the phase relation between a crankshaft and a camshaft in a defined angular range between a maximum advanced and a maximum retarded position. Adapting the timings to the current load and engine speed reduces consumption and emissions. For this purpose, camshaft adjusters are integrated into a drive train via which a torque is transmitted from the crankshaft to the camshaft. This drive train can be designed as a belt, chain or gear drive, for example.
In the case of a hydraulic camshaft adjuster, the output element and the input element form one or more pairs of opposing pressure chambers, which can be supplied with hydraulic fluid. The input element and the output element are arranged coaxially. By filling and emptying individual pressure chambers, a relative motion between the input element and the output element is produced. The spring acting for rotation between the input element and the output element urges the input element in a preferential direction relative to the output element. This preferential direction can be the same as or opposed to the direction of rotation.
One type of hydraulic camshaft adjuster is the vane cell adjuster. Vane cell adjusters have a stator, a rotor and a drive wheel with external teeth. The rotor is designed as an output element, generally in a manner which allows it to be connected for conjoint rotation to the camshaft. The input element comprises the stator and the drive wheel. The stator and the drive wheel are connected to one another for conjoint rotation or, as an alternative, are formed integrally with one another for this purpose. The rotor is arranged coaxially with and within the stator. The rotor and the stator, with their radially extending vanes, define oppositely acting oil chambers, which can be supplied with oil pressure and allow a relative rotation between the stator and the rotor. The vanes are either formed integrally with the rotor or the stator or are arranged as “inserted vanes” in grooves provided for that purpose in the rotor or the stator. Moreover, vane cell adjusters have various sealing covers. The stator and the sealing covers are secured to one another by a plurality of screw connections.
Another type of hydraulic camshaft adjuster is the axial piston adjuster. In this case, a sliding element is moved axially by oil pressure, producing a relative rotation between an input element and an output element by way of helical teeth.
WO 2010/015541 A1 shows a camshaft adjuster having a central valve. The central valve has two inlet ports, wherein one is arranged coaxially with the central valve and the other is arranged radially with respect to the central valve. The inlet ports are designed as bores. The central valve furthermore has two working ports on the outer circumference, which are situated opposite the hydraulic fluid ducts leading to the pressure chambers. Arranged on the side remote from the camshaft is the tank port for returning hydraulic fluid to be displaced into the reservoir of the internal combustion engine.
DE 198 17 319 A1 shows a central valve of a camshaft adjuster. The inlet port is arranged on the outer circumference of the central valve. The inlet port is flanked by the two working ports in the axial direction. The tank port is situated on the end of the central valve adjacent to the camshaft and opens into a radial bore in the camshaft.